In recent years, more and more information has become available on the subsidence of the oceanic lithosphere into the horizons of the transition zone and the lower mantle of the Earth. Highly metamorphosed rocks are often found in ophiolite complexes of folded areas, which, according to some researchers, can also have significant diamond content. A comprehensive study of all possible sources of information about the formation conditions and evolution of contrasting crustal protoliths opens up new prospects for determining such complex geological processes. These studies are also important in the context of identification of new mineralogical and geochemical markers of diamond-forming processes and, on their basis, determination of the possibility of their practical use in improving methods for predicting, prospecting and evaluating diamond deposits. The current issue of our Journal is devoted to these relevant problems.

Research subject. The present evolutionary stage of geodynamic theory is associated with the idea of thermochemical convection of various levels in the Earth's mantle, where the centrifugal branches are represented by plumes, and the centripetal - by subduction zones. Aim. The study of diamonds contributes to an understanding of when, at what level in mantle, under what P-T conditions and geochemical environment particular diamonds originated, which were then transported by centrifugal convection flows to the Earth's surface, thereby permitting characterization of this flow. Materials and methods. Generalization of published materials and characterization of mineral inclusions in diamonds allow the general structure of mantle convection to be clarified in different epochs and different regions. Results. The data obtained on mineral inclusions in diamonds, along with the experimental data on the P-T conditions of their mineral parageneses and geophysical data on mantle properties, indicate that the depth of diamond formation varies from the lower lithosphere in the upper part of the upper mantle (≈150-250 km) to the bottom of the lower mantle. At the same time, the diamonds containing mineral inclusions, characteristic of the lower mantle, account for only the first percents of the general number of diamonds. Conclusions. The transport of diamonds from different depths of their origin is a reliable indication of convection processes (as a plume activity) in the mantle. This information provides evidence to the real existence of plumes, which is important in the context of ongoing discussions on the depth of their origin. However, the study of mineral inclusions in diamonds, particularly in superdeep diamonds, is a challenging task due to the retrograde changes, resorption and sometimes complete dissolution on their way to the surface. These circumstances minimize the probability of occurrence of superdeep diamonds and require consideration when making judgements about the reality of existence of superdeep diamonds.

Research subject. We present the first results on modeling of the interaction of CaCO₃ with metallic Fe in the presence of olivine and serpentine at high P-T parameters in comparison with the CaCO₃-Fe system. The relevance of the study is related to the need to study decarbonatization reactions during subduction of crustal matter into the Earth's reduced mantle within the context of the global carbon cycle. Methods. The experiment was carried out using a BARS high-pressure apparatus at a pressure of 4.0 GPa and temperatures of 1400-1500°С with a subsequent study of the obtained samples on a scanning electron microscope equipped with a chemical microanalysis system. Results. CaCO3 was found to be unstable under the implemented conditions. The reaction products were iron carbide and Ca-wustite or Ca-magnesiowustite in the presence of silicate phases. Conclusions. The interaction of CaCO₃ with metallic Fe at high pressure occurs even if the components are in the solid state. High reaction rates during interaction are provided by the appearance of liquid metal due to the relatively low melting temperature of the eutectic in Fe-C systems. The influence of gravity on the penetration of Fe into the carbonate matrix, which consists in the predominant infiltration of liquid metal between carbonate grains, was established. The presence of H₂O significantly reduces the melting point of carbonate, which leads to an increase in the diffusion of components and decarbonization reaction rate, while the effect of gravity also takes place due to the difference in the density of liquid Fe in comparison with other components in a highly fluidized environment.

Research subject. Mineral inclusions in potassium-bearing tourmaline crystals of the Kumdy-Kol microdiamond deposit. Aim. To reconstruct PT conditions for the origin of potassium-bearing tourmalines. Materials and methods. Mineral analysis and element mapping were performed using an X-ray spectral microanalyzer. Raman spectroscopy was used to detect the C and SiO₂ polymorphs. Results. For the first time, diamond inclusions were identified in tourmalines with the potassium content ranging from 1.0 to 1.6 wt %. In addition, diamond-bearing zircon was detected in tourmaline crystals, with the K₂O content below the detection limit. Previously, diamond inclusions had been exclusively identified only within the most potassium-rich cores of tourmaline crystals, which were approved as a new end member referred to as maruyamaite. Similar to the previous studies, the Kfs inclusions were recognized in both marumaite crystals and tourmaline crystals, with a variable content of potassium. Conclusions. The obtained findings indicate that high-pressure conditions may not be necessary for the formation of potassium-rich tourmaline. The chemical composition of the fluid is most likely to be the main factor controlling the appearance of tourmalines with an unusual composition.

Research subject. Clinopyroxene xenocrysts from the heavy-mineral concentrates of 14 kimberlite bodies (western part of the field: Obnazhennaya, Rubin, Seraya, Vodorazdelnaya, Vtorogodnitsa, Antoshka; central part of the field: Sliudyanka, Skiff II; western part of the field: Irina, Noyabrskaya, Vechernyaya, Lyusya, Dianga and Zhila 79) of the Kuoika field (Yakutian diamondiferous province, Siberian craton). Aim. To reconstruct the mantle paleogeotherms Under the six kimberlite pipes (Vodorazdelnaya, Obnazhennaya, Vtorogodnitsa, Sliudyanka, Dianga, and Zhila 79) using two independent approaches. Materials and methods. The chemical composition of clinopyroxene xenocrysts was investigated and last equilibrium temperatures and pressures were estimated using single-crystal thermobarometry. The geothermal line fitting to the P-T data set was performed using two methods. The first method is based on the D. Hasterok and D.S. Champan model, and the second - on the D. McKenzie model. Results. The value of lithosphere thickness falls within the margin of error for the two methods, being also comparable with earlier reconstructions for the Vtorogodnitsa, Dyanga, and Obnazhennaya pipes. The obtained results indicate that, during the Mesozoic kimberlitic magmatism, the lithosphere thickness beneath the Kuoika field was about 200 km. Conclusion. The determined peculiarities of the chemical composition of clinopyroxene xenocrysts indicate heterogeneity of the lithospheric mantle composition. Different depths of transported mantle material for kimberlite pipes of the Kuoika field, which are coeval and are located a few km apart, may be related to peculiarities of kimberlite magma ascent to the surface and the presence of intermediate magma chambers. The eastern part of the Kuoika field contains more garnet and garnet-spinel peridotites compared to the central and western parts, which may indirectly indicate a greater diamondiferous potential of the eastern block, where the diamondiferous Dianga pipe is located. The absence of diamonds in other discovered pipes of the Kuoika field may be connected with the metasomatic enrichment of the lithospheric mantle in the area of the “diamond window”, which is confirmed by a large number of high-temperature clinopyroxenes at these depths.

Research subject. Spectroscopic features (Raman spectra) of mineral inclusions of peridotite paragenesis (olivine, orthopyroxene, clinopyroxene, garnet) in natural diamonds of the Yakutian diamondiferous province. Materials and methods. A series of diamonds was studied both with single mineral inclusions and with associations of inclusions of peridotite paragenesis. The chemical composition of mineral inclusions in diamonds was determined using an electron probe micro-analyzer (EPMA). The Raman spectra of inclusions were obtained on a spectrometer equipped with a Nd:YAG laser with a wavelength of 532 nm. Results. The revealed spectroscopic characteristics of mineral inclusions in natural diamonds reflect specific features of their chemical composition. Thus, the shift in the positions of the Raman peaks DB1 and DB2 in the olivine spectra reflects the forsterite - fayalite (Mg-Fe) isomorphism; changes in the positions of valence vibrational modes in the Raman spectra of clinopyroxene Si-O_nbr (ν₁₆) and Si-O_br (ν₁₁) and orthopyroxene (ν₁₇) reflect the isomorphism of diopside - jadeite (CaMg-NaAl) and enstatite - ferrosilite (Mg-Fe), position shifts of deformation (ν₂) and valence (ν₁, ν₃) modes of vibrational energies of the Si-O bond in garnets reflect the Al-Cr and Ca-Mg isomorphism, respectively. Conclusions. For the identified correlations, regression lines were calculated, which can be used to determine the quantitative contents of the main chemical components of mineral inclusions (clinopyroxene and garnet) of peridotite paragenesis in situ in diamonds. The developed method for evaluating the chemical composition of garnet and clinopyroxene inclusions can be used to distinguish clinopyroxene and garnet inclusions from different mantle parageneses.

Research subject. The article presents the results of studying 500 diamond crystals from the core of exploration boreholes of crater and diatreme facies of the upper part of V. Grib kimberlite pipe. Crystals from tuffs and tuffites (crater), tufobreccia, autolith kimberlite breccia and porphyry kimberlite (diatreme) were analyzed separately. aim. To carry out a morphological and spectroscopic study of diamonds from V. Grib pipe. Materials and Methods. An VERTEX-70 spectrometer with a Hyperion 1000 microscope was used to determine the total nitrogen concentration and the share of nitrogen in the form of B defects (N_BS), the absorption coefficients of the “platelet” bands B', 3107 cm^-1. Images of photoluminescence (PL) were recorded at 360 nm excitation by an ALROSA VIEW PRO device, in order to detect inhomogeneities and color of PL. The PL spectra were recorded by a Horiba FL-3 spectrometer with an excitation of 350 and 450 nm at 300 K and by an InVia Renishaw spectrometer with an excitation of 405, 488 and 787 nm at 77 K. Results. The distribution of diamonds in terms of nitrogen concentration and NBS is specific; about 50% of the crystals are located along one isotherm, the proportion of low-nitrogen crystals is 5%. The PL spectra of 25% of crystals showed the lines of 883/885 nm of an elementary Ni-containing defect. Most crystals with this defect have less than 400 ppm of nitrogen, but they occupy the entire range according to NBS. This system is found in the spectra of 76% of twins and intergrowth; the latter are of 36% of diamonds with the lines 883/885 nm. The studied diamonds differ from those found in M.V. Lomonosov deposit in terms of a much lower content of crystals of cubic habitus (2 and 15%), a lower degree of dissolution (octahedra, respectively, 33 and 15%), a low proportion of colored stones, as well as a wide range of nitrogen concentration and NBS. Conclusion. The revealed features indicate the specific growth conditions of diamonds from V. Grib deposit, which differed from those of diamonds from other kimberlitic bodies of the East European, Siberian platforms and the Urals. The high proportion of low-nitrogen crystals and Ni-containing diamonds is a possible indicator for the presence of large CLIPPIR-type crystals.

Research subject. Brown diamond crystals from placers of the western slope of the Middle/Northern Urals. Aim. Study of the defect-impurity composition of a sample of brown diamonds from the placers of the western slope of the Middle/ Northern Urals. Methods. In this work, special attention is paid to the analysis of the characteristic spectroscopic features of defects in diamonds from the placers of the western slope of the Middle/Northern Urals using photoluminescence and IR spectroscopy. Results. The studied diamonds from placers of the Middle/Northern Urals are round isometric crystals of a dodecahedral (tetrahexahedral) habitus. According to the results of luminescence (PL) and infrared spectroscopy, three groups of crystals can be distinguished: (i) medium and high nitrogen crystals with low aggregation and dominant defects H3 and 490.7 nm in the PL spectra; (ii) medium and high nitrogen with high aggregation and the predominance of N3 defects in the PL spectra; (iii) low nitrogen with low aggregation and dominant S1 defects in the PL spectra. The first group is characterized by a green glow (excited 405 nm), the second and third groups are characterized by a blue and yellow glow, respectively. The blue glow of the studied crystals is primarily due to the presence of the N₃V center. This defect appears as a result of the aggregation sequence of nitrogen impurities and corresponds to diamonds subjected to the highest temperature annealing (1100-1260°C). Diamonds containing the S1 center are characterized by a low content and aggregation of nitrogen compared to crystals of other groups. Group (i) diamond crystals, whose PL spectra are dominated by the H3 and 490.7 nm systems, have a more intense brown color. Conclusions. The data obtained indicate that annealing at higher temperatures is responsible for the formation of N3V centers in highly aggregated diamonds. The low %B1 aggregation and nitrogen content are associated with the presence of a nitrogen getter (presumably titanium) in the S1 center. An intense brown color appears in the group of diamonds with dominant systems A, H3 and 490.7 nm, which indicates a possible relationship between nitrogen and the corresponding optical absorption.

Research subject. Trap sills of the Daldin-Alakit diamond-bearing region of western Yakutia. Aim. To establish the reason for the influence of sedimentary rocks containing kimberlite diatremes on the introduction of basite magma that forms trap sills and the possibility of using the morphology of sills as a search signs for kimberlites. Materials and methods. Sections of trap sills near kimberlites, their structure, petrographic and petrochemical composition of dolerites performing sills were studied. Results. During the formation of kimberlite diatremes, accompanied by pulsating explosions shifting to the top, a significant compaction of the sedimentary rocks containing kimberlites occurs, associated with thermoelastic stress fields. This process leads to the formation of zones near kimberlites, which are difficult to penetrate for relatively viscous, protocrystalline-enriched basite magmas. When such magmas are introduced, the latter before kimberlites form torus-shaped shafts with a sharply increasing power in intrusions. Sometimes magma, flowing around kimberlites, creates “trappless windows”, occasionally splitting into low-power “tongues”. Quite frequently, before kimberlites, sills crumple, acquiring a wave-like shape. Conclusion. All the listed morphological features of traps arise during the introduction of magma, thus providing an indirect method of searching for kimberlites, particularly during the areal drilling of territories covered by continuous trap fields conducted by ALROSA in Western Yakutia.

Research subject. This paper presents the results of a study of minerals of the apatite group from aillikites of the Zima alkaline-ultramafic carbonatite complex. Aim. To determine the composition of apatites to characterize the studied rocks and to elucidate the patterns of element distribution in the magma of aillikites in the late crystallization stages. Materials and Methods. Minerals of the apatite group from 6 samples (4 from dikes of the Bol'shetagninsky massif, 1 from the Bushkanai dike, 1 from the Beloziminskaya pipe) were studied. The samples showed similar textural-structural features, differing in the mineral composition of the groundmass. Results. Minerals of the apatite group are widespread in the groundmass of all the studied rocks. They are characterized by idiomorphic, subidiomorphic crystals of homogeneous composition, 10-100 microns in size. Minerals of the apatite group were identified as fluorapatite and hydroxyapatite characterized by a significant SiO₂ content (up to 5 wt %), low SrO content (up to 1.5 wt %) and REE₂O₃ (up to 2 wt %). The studied apatites also include MgO, FeO, Na₂O, SO₄, and CO₃. Fluorapatites from dyke aillikites are characterized by a higher silicon content as compared to apatites from the Beloziminskiy pipe. Apatites from fresh aillikites of the Bushkanai dyke have a relatively higher content of Sr, REE, and F than minerals from serpentinized samples. Conclusions. The composition of the studied apatites has a lower Sr and Ba content than orangeite and lamproite apatites. In terms of Sr, Si and REE contents, the studied apatites are similar to kimberlite and ailikite apatites. Such a difference allows minerals of the apatite group to be used as an indicator mineral for classification of kimberlites and related rocks, but only in combination with petrography and composition of other minerals of the groundmass.

Research subject. Detrital zircons from sandstones that contain no admixtures of magmatic material, sampled from the crater parts of the highly diamondiferous V. Grib kimberlite pipe and KL-01 magmatic object. Both objects are located in the north of the East European Platform, within the Arkhangelsk diamondiferous province, at a distance of ≈100 km from each other. Aim. To obtain the first data on the composition of the U-Pb isotope system of detrital zircons from sandstones of magmatic objects of the Arkhangelsk diamondiferous province in order to evaluate the ages of their sources and reveal correlations with known tectono-thermal events in the continental crust of the region. Materials and methods. Using the LA-ICP-MS method, data were obtained on the composition of the U-Pb isotopic system of 52 zircon grains from the sandstones of the V. Grib pipe and 143 zircon grains from the KL-01 sandstones. Results. Sources of various ages from Archean to Neoproterozoic were established for the studied zircons. However, the majority zircons have Mesoproterozoic age, namely 63 and 65% of grains from the V. Grib pipe and KL-01 object, respectively. The sandstones of the V. Grib pipe contain a larger amount of Meso- and Neo-Archean zircons (≈15%) and a smaller amount of Paleoproterozoic grains (≈14%) compared to those from the KL-01 object ≈7 and 20%, respectively. The population of zircons with the U-Pb ages of 900-700 Ma is absent in the two objects. The minimum age of zircons from sandstones of the crater of the V. Grib pipe (557 ± ± 9 Ma) and KL-01 object (609 ± 9 Ma) is consistent with that of formation of the Vendian sandstones in the area of the pipes of the Arkhangelsk diamondiferous province. Conclusions. The obtained U-Pb age for the studied detrital zircons generally correlate with the previously identified stages of tectono-thermal events in the continental crust of the northern territories of the East European Platform, with the exception of the Mesoproterozoic period 1.7-1.4 and 1.3-1.0 Ga ago, which corresponds to the predominant part U-Pb age values of the studied zircons.

Research subject. Morphology of garnet xenocryst grains from the crater and diatreme parts of the highly diamondiferous V. Grib kimberlite pipe of the Arkhangelsk diamondiferous province. Aim. To reconstruct the main stages of endogenous and exogenous morphogenesis of garnet xenocrysts from the crater and diatreme parts of the kimberlite pipe based on a detailed study of their morphological features. To demonstrate the applicability of the data obtained in the interpretation of the morphology of grains of kimberlite indicator minerals from modern alluvial sediments during prospecting and exploration for diamonds in the north of the East European Platform. Materials and methods. A detailed study of the morphology of 655 garnet grains was carried using the methods of optical and electron-scanning microscopy. Garnet grains were selected from the heavy mineral concentrate of crushed rocks, representing the crater (sandstones) and diatreme (kimberlite) parts of the V. Grib pipe. All visually diagnosed garnet grains were handpicked selected from the rocks of the crater part, extracted from the core of one borehole and representing an interval from 70 to 174 m from the surface. For comparison, out of 1100 grains of garnet xenocrysts, selected by random sampling from the concentrate of minerals of the heavy fraction of kimberlite of the diatreme part, 180 garnet grains were selected, representing four-color groups: purple, red, red-orange and orange. Results. The majority of garnets from the crater (96%) and diatreme (89%) parts of the V. Grib kimberlite pipe were shown to exhibit the “primary” magmatic morphology. Nevertheless, the garnet grains with well-developed pyramidal shingle-like (3% in the crater and 11% in the diatreme) and drop-shaped (1% in the crater) reliefs have been identified. These types of garnets were formed under the influence of postmagmatic processes. For the first time, in the deep diatreme part of the pipe (more than 200 m from the surface), composed of dense kimberlite, garnets with a well-developed pyramidal shingle-like relief were found, which had been previously interpreted for the East European Platform only as components of the secondary deposits or the upper horizons of the crater parts of the pipes. Conclusions. Garnets with a well-developed pyramidal shingle-like relief, found in modern alluvial sediments, can be interpreted as from a secondary deposit only if they show signs of mechanical abrasion; the absence of traces of mechanical abrasion on such grains does not allow us to exclude the proximity of the primary source. The presence of drop-shaped relief garnets in the crater of the V. Grib pipe (150-168 m from the surface) also calls into question the unambiguous interpretation of such grains as a sign of secondary deposits: only the maximum degree of chemical abrasion of garnets with the formation of cuboids grains can indicate their redeposited nature. The results confirm the need to improve the method of prospecting for diamond deposits according to the typomorphic features of kimberlite indicator minerals recovered from the modern sediments, sampled in the north of the East European Platform.

Research subject. To characterize the Sylva fluidogenic-explosive complex, which was established in the junction area of the West Ural thrust megazone (head of the Sylva River) and the eastern wing of the Yuryuzano-Sylva depression of the Pre-Ural trough. Materials and methods. The authors' materials collected during research works at GSA200/2 sheet O-40-XXIX (Shalinskaya Ploshchad), as well as those collected during the work under the Priority 2030 Federal Program, were used. Data on the geology, petrochemistry, petrography, structural and tectonic position of clastogenic rock associations in the area of influence of the Main West Ural thrust were employed. Experimental data were obtained using a TESCAN VEGA LMS electron microscope equipped with an Xplore 30 energy dispersive X-ray spectroscopic prefix, and an URS-55 X-ray unit (Ural State Mining University), as well as CPM-35 and Shimadzu EDX-8000 spectrometers and an XRD-7000 diffractometer (Geoanalitik Centre, Zavaritsky Institute of Geology and Geochemistry of the Ural Branch of the Russian Academy of Sciences). Results. For the first time, the mineralogical-petrographic and chemical compositions of diamond-bearing rocks of the Sylva fluidogenic complex were established. Diamonds and minerals contained in the studied rocks were determined by XRD (sanidine, analcime, etc.). The conducted analysis of the rocks suggests their possible fluid-magmatic genesis, which is indicated by mineralogical features, including accessory minerals-indicators of diamond content, the presence of ellipsoid and teardrop-shaped volcanic glass, finely-dispersed bulk and poorly-rolled unsorted fragments of igneous and sedimentary rocks. Conclusions. The results obtained indicate the possibility of manifestation of Early Mesozoic phreatic volcanism in the studied area, which led to the transfer of the Sylva diamond complex and accessory minerals by fluidolites.

Research subject. Diamondiferous explosive detrital and sedimentary volcanoclastic rocks of the Carnian base of the Upper-Triassic confined to the west flank of the Bulkur Anticline in the north-eastern Siberian Platform. Aim. To identify diamondiferous features of Carnian rocks. Materials and methods. The materials collected by the authors while performing prospecting and evaluation works by the OOO Arctic Mining Company in 2022-2023 were used. The materials were represented by field observation results and mineral-petrographic studies. Rock types were defined by petrographic analysis in thin sections using a Leica DM2700P microscope and known classifications. Diamonds and accessory minerals were distinguished from steam sediment samples and described at the central analytical laboratory of the Vilyuysk Geosurvey Expedition, PJSC Alrosa. The estimation of diamond and pyrope content in core- and bulk samples (CPT) was performed considering their direct correlation. Results. The highest concentrations of diamonds were found to be localized in rocks in the west flank of the Bulkur Anticline. These formations were detected in lapilli tuffs, xenotuff breccia and orthotuffites. Paratuffites and tuff aleuro-sandstones exhibit a lesser diamond potential. Conclusions. The diamond potential of rocks of the Carnian base correlates well with the pyrope content and saturation of volcanoclastic materials. Tuff aleuro-sand-stones of the Bulkur member in the Osipay base and overlying shell deposits are considered potentially diamondiferous. Diamondiferous formations possess considerable thickness and productive efficiency, thus assuming a substantial increase in the diamond prospective potential in the Russian Arctic.

Research subject. The placer diamond deposit of the Morgogor River, Anabar, Yakutia. The geological history of this deposit has not been reliably established, and the root sources remain unknown. Aim. To describe the mineralogical and spectroscopic characteristics of diamonds from the Morgogor river deposit in comparison with the previously studied diamonds from the Ebelyakh river placer. To divide the studied diamonds into genetic groups, presumably reflecting the primary sources of demolition, according to the distribution of A-centers. To assess the stability of mineralogical and spectroscopic features for the identification of genetic groups. Materials and Methods. Data on 1386 diamond crystals mined from 1978 to 2018 were used. Detailed descriptions were made for 1168 of them; IR spectroscopic studies were carried out for 103 diamonds; informative EPR spectra were obtained for 61 diamonds. Results. Using IR spectroscopy data, the Morgogor diamonds were divided into three groups based on the content of A-centers according to the methodology previously developed for the study of Ebelyakh diamonds. The diamonds of the studied groups differed significantly in terms of the habitus and morphology of crystals, the development of plastic deformation processes, the content of inclusions, the presence and diversity of visual luminescence, as well as associations of paramagnetic centers. The difference between the Morgogor and Ebelakh samples consisted in the ratio of the shares of genetic groups, which can be interpreted as the influence of a geographical factor, i.e., location in relation to the sources and directions of demolition at all stages of placer formation. Conclusions. The diamonds of the Morgogor river have the same three primary sources as the diamonds of the Ebelakh river. Statistical separation of crystals by primary sources - genetic groups - is possible based on the distribution of the content of A-centers. This separation forms groups, whose diamonds differ not only in IR characteristics, but also in the morphological features and the nature of luminescence. The statistically significant samples of diamonds from various Anabar placers differ in the ratio of the shares of genetic groups, which reflects their geographical location, adjusted for the directions of demolition in the processes of formation and redeposition of placers. The data obtained can be used to identify the directions of demolition and, ultimately, to search for its primary sources.

Research subject. The Takata formation of the Emsian tier of the Lower Devonian (D₁tk) in the Urals is a reservoir of Devonian diamonds. Aim. Confirmation and determination of the diamond-bearing conditions of the reservoir. Materials and Methods. Generalization of primary and interpreted geological information. Lithofacial analysis. Historical and geological reconstruction. Cartographic analysis and geological and cartographic modeling in the ArcMapESRY GIS environment using the ModelBuilder module. Results. The Takata formation is part of the Emsian tier of the Lower Devonian. Tectonically, the Takata formation is located in the West Ural Folded Zone. The diamond content in the Urals is spatially related to the outputs of the Takata formation. The industrial diamond-bearing capacity and the highest density of diamond placers are located in the Vishersky, Chykmansky and Chusovskoy diamond-bearing regions of the Northern and Middle Urals within the Perm Krai. In the early Devonian, the Takata Sea existed in the Vishera diamond-bearing area; a large river with a delta flowed in the direction from northwest to southeast. The sediments of the formation comprise the facies cycle: flood-plain - channel alluvium - delta sediments - underwater-delta - marine sediments. Diamonds are concentrated in the thickness of coarse-grained alluvium, small-pebble basal conglomerates that formed on the land-sea boundary of the paleocontinent of the Russian Plate. Three facies types of the Takata formation section are distinguished: continental, coastal-marine and marine. Its diamond-bearing capacity is associated with the continental and coastal-marine sediments of the formation within the Perm Region. To the north and south of the diamond-bearing areas of the Perm Krai, the Takata formation is represented by marine sediments. According to the geodynamic model based on the geological section of the Northern Urals, the alluvial and coastal-marine Takata diamond placers were formed in the early Devonian as a result of the demolition of material from the Russian Plate. The sources of destruction were rocks of the Precambrian, Ordovician and Silurian. The main spatial-geomorphological criterion for searching for diamond-bearing conglomerates of the Takata formation is the maximum distance of demolition from these conglomerations to placers, equal to 500 m.

Research subject. Geological features of the structure and composition of the Syuzevskoye diamond placer in the Aleksandrovsky region of the Perm Krai. The placer was found in the border zone of two regional tectonic structures of the Urals: the Western Ural outer folding zone and the Central Ural uplift. This placer was developed within the erosion-karst (?), erosion-structural or tectonically determined Chikman-Nyarskaya depression. Materials and methods. The placer was identified in the period from 2017 to 2022 during a geological study of the subsoil area “Glubokiy” (License PEM 02687 KP LLC “Almining”). Mining and enrichment works were carried out according to the original enrichment scheme using the clamshell sampling method, heavy media and electromagnetic separation. The morphometric characteristics of several hundred diamonds were identified and described; reports were prepared; and reserves were assessed. Results. In the section of the Syuzevskoye placer, two diamond-bearing strata are clearly distinguished, separated by poor- and non-diamond-bearing deposits; anomalously high seam thickness for the Ural placers (up to 14-16 m) was established; high areal productivity of the placer (up to 0.7-1.2 ct/m²) and high diamond content (up to 0.5 ct/m³ per sample and an average of 0.09 ct/m³ for the placer). The placer is attributed to the type of placers of tectonic scarp zones. Reserves of alluvial diamonds weighing 430.5 thousand ct of the Syuzevskoye deposit are estimated at C₁ + C₂ categories in the area limited by the area between exploration lines 107-116 (size 1000 x 750 m); approved by the Minutes of the GKZ Rosnedra No. 7139 dated November 18, 2022 and will be increased. Certificate No. PEM 23 DRK 10147 confirming the discovery of a mineral deposit, issued by the Federal Agency for Subsoil Use of the Russian Federation to LLC Almining on March 29, 2023. Over 90% of diamonds are of gem quality. The average mass of crystals in the reserve calculation loop is 87 mg, and behind the loops is 29 mg. The leading size classes by mass -8 + 4 and -4 + 2 mm are 93.9% and 72.3% in quantity with an average mass of a diamond crystal of 99.9 mg. The shape is dominated by dodecahedroids (66.9%), less fragments of crystals with an unpreserved shape (14.9%) and fragments of crystals (13.1%); octahedrons (2.4%) and tetrahedroids (2.2%) are rare, rhombic dodecahedroids (0.4%) are rare. The preservation of crystals is good: full crystals make up 63.7%, fragments of crystals - 16.3%, fragments - 12.9%. Most of the crystals do not have wear (42.4%), or have weak wear of the tops and ribs (43.0%), medium and strong wear was noted only in 13.7% of the crystals. The average cost of diamonds is estimated at 361.59 USD per 1 ct. Conclusions. A unique deep-seated diamond deposit has been discovered, which is considered as a new type of deep-seated diamond-bearing placers in tectonic ledge zones. The geological criteria for identifying such diamond deposits in the Urals were determined. A new technological scheme for prospecting and exploration of deep-seated diamond placers within erosion-karst and tectonically determined depressions was developed, which is applicable for prospecting for precious metal placers.